Question for a machinist

patooyee · Dec 14, 2014

I have a really nice chuck that came with my lathe but it didn't come with a back plate. My lathe nose taper is L1. So I bought a semi-finished back plate and turned it down to size. But I screwed up on the last cut and went a few thou too deep causing the back plate to be just a few thou too small for the bore on the back of the chuck. Mad as hell at myself for doing it on a $200 back plate. I'm trying to figure out a suitable way to salvage it. Some ideas I've thought of are to get some shim stock and wrap it around the OD to take up the few thou in slack or to weld around the entire back plate dia. to add material and then re-machine it. The back plate is cast iron though and I'm not sure what an appropriate welding process would be or if I can easily cut on a weld. (I can TIG or MIG if needed though.)

Short of trashing the back plate what would a real machinist do?

krackem · Dec 14, 2014

I know cast must pre heat, tig welded with nickle or( not sure on spelling) enconel Wire and post heat not sure on temps I'll ask the main qc at work Tuesday and I'll let or machinest read this and get his opinion (30+ years) if someone hasn't got you an answer by then is it regular old cast and if qc says enconel wire is best I can get us some from work it's expensive wire and how much is a few thousandths

mac · Dec 14, 2014

so are you referring to the shank side of backing plate? if so, maybe you could take some appropriate sized DOM and turn backing plate shank down some more, to a press fit in the tubing. essentially making a speedy sleeve. then re-turn backing plate shank back to desired diameter. maybe missing completely what your going for. pictures would help if this does not sound like it would work.

patooyee · Dec 14, 2014

Here's the exact back plate:

The chuck has a bore in the back of it and the OD of that bore should be a snug, almost press fit onto the OD of the above back plate. Just judging by your description of the "shank" I'm thinking you are understanding me correctly because the DOM idea would probably work except that it would have to be like 7" ID DOM. That's not really a huge problem to find, just not something I keep on hand. Its definitely an option though.

bjeep · Dec 14, 2014

What is a few .002-.003 or more?

patooyee · Dec 14, 2014

I had to move onto another project so I didn't measure before I left the shop. But if I had to estimate I would say .003 or so. Just barely enough to feel / see and you really have to be looking closely.

jccarter1 · Dec 14, 2014

Check this place out cheap stuff but pretty nice quality

http://www.shars.com

patooyee · Dec 15, 2014

Re: Re: Re: Question for a machinist

mac said:
so are you referring to the shank side of backing plate? if so, maybe you could take some appropriate sized DOM and turn backing plate shank down some more, to a press fit in the tubing. essentially making a speedy sleeve. then re-turn backing plate shank back to desired diameter. maybe missing completely what your going for. pictures would help if this does not sound like it would work.

The more I think about this the better it sounds. I think this is the route I will go. Thank you.

Elliott · Dec 15, 2014

Is this a straight cut or a taper cut, that is different from both my lathes, but if it is a taper cut you could machine some off of the back side. If it is a straight cut, just bolt it on, dowel it, and cut your jaws in to make sure they are true. But all of this is said without me understanding how this bolts up on the lathe so it may not help at all.

patooyee · Dec 15, 2014

Re:

Straight.

bjeep · Dec 15, 2014

Knurling will make the OD larger but not by much. I have used it to fix parts. Don't know how well it will work in this situation.

patooyee · Dec 15, 2014

This isn't the exact chuck I am working with but the picture is a good representation of what the back of my chuck looks like:

Elliott, I've been wanting to cut the jaws on another chuck that I have as well as true this one up when I get it mounted but I don't have a tool post grinder and I believe all the jaws are hardened. Is there another acceptable method?

Elliott · Dec 15, 2014

I would use a carbide inserted bit, You just need to chuck something up by clamping on the inside of a round piece, you will need something with enough opening that you have the jaws open enough to run your bit in.

patooyee · Dec 15, 2014

Re: Re: Question for a machinist

Elliott said:
I would use a carbide inserted bit, You just need to chuck something up by clamping on the inside of a round piece, you will need something with enough opening that you have the jaws open enough to run your bit in.

Thanks. Kind of what I had in mind.

84mallcrawl · Dec 15, 2014

why not cut the OD that is too small now down another .030-.040 and rebuild with gas welded brass

ldwoodruff · Dec 15, 2014

cut your back plate o.d down more, make a sleeve o.d bigger then the size you need, press it on and machine it down so it all runs true, problem solved!!!

chembree · Dec 15, 2014

TRY THIS STUFF OUT IT IS A MIRACLE IN A JUG

http://www.belzona.com/en/products/purpose/metal-repair.aspx

Eddyj · Dec 15, 2014

They have it for rubber. I wonder if it could work as a patch for tires?

patooyee · Dec 15, 2014

ldwoodruff said:
cut your back plate o.d down more, make a sleeve o.d bigger then the size you need, press it on and machine it down so it all runs true, problem solved!!!

This is what I am going to do. I feel like it is the ideal solution.